With the increasing prominence of the feminist movement in the 1970s, many women began to speak out and demonstrate against the pornography industry, claiming it exploited women and women's bodies and encouraged violence against women. (Bettmann/Corbis)

Sexually explicit expression has been subject to legal regulation in the United States since the earliest days of the republic. Until the last half of the twentieth century, legal sanctions imposed on sexually explicit expression were not thought to conflict with the free speech protections of the First Amendment. Beginning in the 1950s, however, the U.S. Supreme Court began recognizing that a large amount of speech containing sexually explicit content also had significant First Amendment value. The Supreme Court therefore began limiting the government's power to regulate or ban certain types of sexually explicit speech.

Under the Supreme Court's modern cases, what is popularly...